Hawks and Eagles in Denmark

An insight to their habitat and what effect conservation efforts have

Rakul Maria Hjalmarsdóttir Tórgarð

Disclaimer

The following project was developed as a part of the final exam in the course Social data analysis and visualization taught at DTU in spring 2025.

The explainer notebook can be found here.

Introduction

The Danish Ornithology Community (Dansk Ornitologisk Forening, or DOF) was founded in 1906, with the goal of protecting birds and their habitats in Denmark. Over the years, DOF has played a crucial role in bird conservation efforts, including monitoring bird populations, advocating for environmental policies, and raising public awareness about the importance of biodiversity. Their work has been instrumental in understanding the trends and challenges faced by bird species in Denmark. DOF’s current visions are primarily to protect wild birdlife in Denmark and improve their habitat, and to collect and inform knowledge of birds to the people.

One of the major things that DOF has done, is to allow people to register their own observations of birds via their website, DOFBasen.dk. This has had a huge impact on spreading the knowledge of bird species and their habitats across Denmark. By enabling citizens and volunteers to contribute their observations, DOF has created a rich dataset that provides valuable insights into bird populations and their trends over time.

Project Eagle and Project Montagu’s harrier

In extension to their work on bird conservation, DOF has for the past couple of years worked with various focus projects, two of them being Project Eagle and Project Montagu’s Harrier. The following sections will take a closer look at what impact these projects have had on the population of the bird species in these projects. The birds inspected in this sections are

From Project Eagle:

  • The white-tailed eagle
  • The golden eagle
  • The osprey

From Project Montagu’s Harrier:

  • The Montagu’s Harrier (surprise!)

The dataset used in the following sections contains all observation registered on DOFBasen.dk from 1998 - 2024 of these species [1].

But what do these birds look like?

Before diving into each bird specie, let’s first take a look at each bird, to gain a better understanding of what we’re about to inspect.

But what do these birds look like?

Before diving into each bird specie, let’s first take a look at each bird, to gain a better understanding of what we’re about to inspect.

White-tailed eagle

  • The largest eagle in Denmark (And the whole of Europe!), with an average wing-span of 200-245 cm
  • Greyish mid-brown colour overall, with a beak that goes from brown’ish to yellow as the bird ages

White-tailed eagle

But what do these birds look like?

Before diving into each bird specie, let’s first take a look at each bird, to gain a better understanding of what we’re about to inspect.

Golden eagle

  • The second-largest eagle in Denmark, with an average wing-span of 190-227 cm
  • Primarily lives off smaller birds and other mammals, such as mice

Golden eagle

But what do these birds look like?

Before diving into each bird specie, let’s first take a look at each bird, to gain a better understanding of what we’re about to inspect.

Osprey

  • Quite characteristic with a white/grey underpart and brown upperpart
  • Primarily lives off fish, which is why it’s also known as the Sea Hawk

Osprey

But what do these birds look like?

Before diving into each bird specie, let’s first take a look at each bird, to gain a better understanding of what we’re about to inspect.

Montagu’s Harrier

  • Small bird of prey, with an average wing-span of 98-110 cm
  • A quite rare migratory bird, which visits Denmark in summertime

Montagu's harrier

Overall development

If we look at the overall development of these birds over time, it is clear that there has been one specie who has shown remarkable success in expanding their population from 1998 - 2024; the white-tailed eagle.

Recovering from extinction

The white-tailed eagle bred in Denmark until it was driven by extinct by persecution in 1912. After this it made a number of breeding attempts during the second half of the 20th century, unfortunately usually unsuccessful. It was clear that some action had to be taken, in order to reestablish the White-tailed eagle.

Inspired by similar projects run in Sweden and Germany, DOF initiated Project Eagle in 1991, hoping that this might ultimately lead to reestablishment of the population [2].

White-tailed eagle

Conservation efforts and their positive effect

The project achieved to promote a positive attitude among Danes towards the eagles, which established themselves in Denmark from 1995 onwards. The first succesfull breeding attempt occoured in 1996 [2].

Although the specie had a smaller drawback around the turn of the century, the overall development of the species has been upward.

Registered observations

With this successfull breeding attempt in 1996, an increase in the species population began to take effect.

The map on the right illustrates the development over time of the White-tailed eagle in Denmark. Initially a rare species, limited to a few specific regions, the White-tailed eagle has expanded significantly and is now widespread across the Danish landscape.

Conclusion

Thanks to DOF’s initiatives taken in Project Eagle, which were implemented around the same time and in similar ways to conservation efforts in neighbouring countries such as Germany and Sweden, this ultimately contributed to the species’ successful recovery [3].

Today the White-tailed eagle is on the Dansih Redlist, marked in the category NT, Near Threathened [4]. There are 151 active breeding pairs [5].

White-tailed eagle (young)

Project Montagu’s harrier

The Montagu’s harrier is a relatively new bird in Denmark. Unlikely the White-tailed eagle, which resides in Denmark year-round, the Montagu’s harrier is a breeding bird. This means that the bird only visits Denmark for its breeding season, which is from spring to late summer.

History lessons

The first appearance of the Montagu’s harrier in Denmark dates back to the early 1900s. Over the following decades, its population grew significantly. By the 1940s and 1950s, there was an estimate of 350 to 400 breeding pairs in the country. However, since then the population has declined, and today there are only about 20-30 breeding pairs registered [6].

A montagu harrier on a stick

A threathened life

One of the primary reason for this decline is the substantial change in its habitat. The Montagu’s harriers nested in natural wetlands such as swamps and moorlands. But as these habitats have been increasingly replaced by agricultural land – especially corn and rapeseed fields – the harriers have adapted by nesting in these cultivated areas. When the birds arrive in April, the fields appear to be suitable nesting sites, offering shelter and camouflage for their nests and chicks.

However, this adaptation has come with significant risks. The nests are vulnerable to both natural predators, such as foxes, and to human agricultural activity. When farmers harvest their corps later in the summer, the nests can be destroyed, putting the young birds in danger [7].

DOF’s effort

To help protect the Montagu’s harrier, DOF launched Project Montagu’s harrier in 1995 [8]. Since then, DOF has stepped in every year during the breeding season. When a nest is discovered on private land, volunteers and researchers work closely with the local landowners, informing them about the birds and encouraging their support in safeguarding the nest. Most often, this involves setting up a small protective fence around the site. These fences not only help keep predators away, but also make it easier for farmers to manage their harvest around the nests without disturbing the birds [8]. The video below, which us published by DOF, explains more about the project.

How has the effect been?

Since the conservation project began in 1995, the population of the Montagu’s Harrier has been steadily increasing. Despite this encouraging trend, the species is still listed as Endangered (EN) on the Danish Red List. This means that without ongoing protection efforts, the Montagu’s Harrier could face extinction in the near future [9].

Registered observations

The Montagu’s harrier is most commonly found in southwestern Jutland, particularly near the Wadden Sea. This is because the species primarily inhabits central and southern Europe, making Denmark the northern edge of its breeding range [7].

Some of the observations are registered in Skagen, and especially since 2021, a lot of harriers have been observed in Borris Hede [10].

Conclusion

The Montagu’s harrier is listed under Annex I of the EU Birds Directive, which means that all countries where the species occurs are legally obligated to protect the species and its habitats.

In Denmark the species is listed as Endangered (EN) [9], a status it has held since Denmark in 2010 began applying the IUCN’s international Red List categories and criteria [11]. This highlights the importance of the conservation efforts carried out by DOF and supported by local communities.

Montagus harrier

References

1.
GBIF.Org User (2025) Occurrence download
2.
Ehmsen E, Pedersen L, Meltofte H, Tscherning C, Nyegaard T (2011) The occurrence and reestablishment of white-tailed eagle and golden eagle as breeding birds in denmark. Dansk Ornitologisk Forenings Tidsskrift 105:139–150
3.
4.
Moeslund JE (2024) Den danske rødliste
5.
6.
7.
8.
Nyegaard T (2024) Hedehøg - projekt hedehøg
9.
Nielsen P, Nielsen A, Rasmussen LM (2021) Hedehøg
10.
11.
Moeslund JE (2024) Om rødlisten